Glass ceramic having specific thermal expansion characteristics

ABSTRACT

The present invention relates to a glass ceramic having improved thermal expansion characteristics and to the use thereof in a precision component.

The present invention relates to a glass ceramic having specific thermalexpansion characteristics and simultaneously good meltability, shapingand ceramizability, and to the use of the glass ceramic according to theinvention in a precision component.

BACKGROUND OF THE INVENTION

Materials and precision components having low thermal expansion or lowCTE (coefficient of thermal expansion) are already known in the priorart.

Known materials for precision components having low thermal expansion inthe temperature range around room temperature are ceramics, Ti-dopedquartz glass and glass ceramics. Glass ceramics having low thermalexpansion are especially lithium aluminium silicate glass ceramics (LASglass ceramics), which are described, for example, in U.S. Pat. Nos.4,851,372, 5,591,682, EP 587979 A, U.S. Pat. Nos. 7,226,881, 7,645,714,DE 102004008824 A, DE 102018111144 A. Further materials for precisioncomponents are cordierite ceramics or cordierite glass ceramics.

Such materials are frequently used for precision components that have tofulfil particularly strict demands in relation to their properties (forexample mechanical, physical, optical properties). They are usedespecially in terrestrial and space-based astronomy and observation ofthe Earth, LCD lithography, microlithography and EUV lithography,metrology, spectroscopy and measurement technology. It is a particularrequirement here for the components, according to the specificapplication, to have extremely low thermal expansion.

In general, the thermal expansion of a material is determined by astatic method in which the length of a test specimen is determined atthe start and at the end of the specific temperature interval, and thedifference in length is used to calculate the average coefficient ofexpansion a or CTE (coefficient of thermal expansion). The CTE is thenreported as the average for this temperature interval, for example forthe temperature interval from 0° C. to 50° C., as CTE(0;50) or α(0;50).

In order to meet the constantly growing demands, materials having a CTEbetter matched to the field of use of a component formed from thematerial have been developed. For example, the average CTE can beoptimized not just for the standard temperature interval CTE(0;50), butalso, for example, for a temperature interval around the actualapplication temperature, for example the interval from 19° C. to 25° C.,i.e. CTE(19;25), for particular lithography applications. As well as thedetermination of the average CTE, it is possible to determine thethermal expansion of a test specimen in very small temperature intervalsas well, and hence to represent them as a CTE-T curve. Such a CTE-Tcurve can preferably have a zero crossing at one or more temperatures,preferably at or close to the planned application temperature. At a zerocrossing of the CTE-T curve, the relative change in length with changingtemperature is particularly small. In the case of some glass ceramics,such a zero crossing of the CTE-T curve can be shifted to theapplication temperature of the component by suitable thermal treatment.As well as the absolute CTE value, the slope of the CTE-T curve aroundthe application temperature should be as low as possible in order tobring about a lowest possible change in length of the component in theevent of slight temperature changes. The above-described optimizationsof the CTE or of thermal expansion, in the case of these specificzero-expansion glass ceramics, are generally effected with unchangedcomposition by variation of the ceramization conditions.

An adverse effect in the case of the known precision components andmaterials, especially in the case of glass ceramics such as LAS glassceramics, is “thermal hysteresis”, called “hysteresis” hereinafter forshort. What is meant here by hysteresis is that the change in length ofa test specimen in the case of heating at a constant heating ratediffers from the change in length of the test specimen in the case ofsubsequent cooling at a constant cooling rate, even though the absolutevalue of cooling rate and heating rate is the same. If the change inlength is presented as a graph as a function of the temperature forheating and cooling, the result is a classic hysteresis loop. The extentof the hysteresis loop also depends on the rate of temperature change.The faster the change in temperature, the more marked the hysteresiseffect. Hysteresis effect makes it clear that the thermal expansion of aLAS glass ceramic depends on temperature and on time, i.e., for example,on the rate of temperature change, for which there have also beensporadic descriptions in the specialist literature, for example O.Lindig and W. Pannhorst, “Thermal expansion and length stability ofZERODUR® in dependence on temperature and time”, APPLIED OPTICS, vol.24, no. 20, October 1985; R. Haug et al., “Length variation in ZERODUR®M in the temperature range from −60° C. to +100° C.”, APPLIED OPTICS,vol. 28, no. 19, October 1989; R. Jedamzik et al., “Modeling of thethermal expansion behavior of ZERODUR® at arbitrary temperatureprofiles”, Proc. SPIE Vol. 7739, 2010; D. B. Hall, “Dimensionalstability tests over time and temperature for several low-expansionglass ceramics”, APPLIED OPTICS, vol. 35, no. 10, April 1996.

Since the change in length of a glass ceramic exhibiting thermalhysteresis is delayed or advanced with respect to the change intemperature, the material or a precision component manufacturedtherefrom has a troublesome isothermal change in length, meaning that,after a change in temperature, a change in length of the material occurseven at the time when the temperature is already being kept constant(called “isothermal hold”), until a stable state is attained. If thematerial is then reheated and cooled, the same effect occurs again.

With the LAS glass ceramics known to date, in spite of variation of theceramization conditions with unchanged composition, it has not beenpossible to remedy the effect of thermal hysteresis without adverseeffects on other properties.

In relation to the properties of materials, especially glass ceramics,for use in precision components, a relevant temperature range is from 0°C. to 50° C., especially from 10° C. to 35° C. or from 19° C. to 25° C.,with a temperature of 22° C. generally being referred to as roomtemperature. Since many applications of precision components take placewithin the temperature range from greater than 0° C. to roomtemperature, materials having thermal hysteresis effects and isothermalchanges in length are disadvantageous, since there can be opticalfaults, for example, in the case of optical components such aslithography mirrors and astronomical or space-based mirrors. In the caseof other precision components made of glass ceramic that are employed inmeasurement technology (e.g. precision measurement scales, referenceplates in interferometers), this can cause inaccuracies in measurement.

Some known materials such as ceramics, Ti-doped quartz glass andparticular glass ceramics feature an average coefficient of thermalexpansion CTE (0;50) of 0±0.1×10⁻⁶/K (corresponding to 0±0.1 ppm/K).Materials having such a low average CTE within the temperature rangementioned are referred to as zero-expansion materials in the context ofthis invention. However, glass ceramics, especially LAS glass ceramics,having such an optimized average CTE generally have thermal hysteresiswithin the temperature range of 10° C. to 35° C. In other words,specifically in applications around room temperature (i.e. 22° C.), adisturbing hysteresis effect occurs in the case of these materials,which impairs the accuracy of precision components produced with such amaterial. Therefore, a glass ceramic material has been developed (seeU.S. Pat. No. 4,851,372) that has no significant hysteresis at roomtemperature, although the effect has not been eliminated, but merelyshifted to lower temperatures, such that this glass ceramic attemperatures of 10° C. or lower shows distinct hysteresis that canlikewise still be troublesome. In order to characterize the thermalhysteresis of a material within a particular temperature range, in thecontext of this invention, therefore, the thermal characteristics of thematerials are considered for different temperature points within thisrange. There are even glass ceramics that show no significant hysteresisat 22° C. and at 5° C., but these glass ceramics have an average CTE(0;50) of >0±0.1 ppm/K, i.e. are not zero-expansion glass ceramicswithin the scope of the abovementioned definition.

A further demand on a glass ceramic material is good meltability of theglass components, and simple melt guiding and homogenization of theunderlying glass melt in industrial scale production plants, in order—oncompletion of ceramization of the glass—to meet the high demands on theglass ceramic with regard to CTE homogeneity, internalquality—especially a low level of inclusions (especially bubbles), lowlevel of streaks—and polishability etc.

It was thus an object of the invention to provide a glass ceramic havingimproved expansion characteristics. A further object was to provide aglass ceramic producible on an industrial scale that has zero expansionand reduced thermal hysteresis, especially within the temperature rangeof 10° C. to 35° C., and a precision component produced from saidmaterial.

The above object is achieved by the subject-matter of the claims. Thepresent invention has various aspects:

In one aspect of the invention, an LAS glass ceramic is provided, whichhas an average coefficient of thermal expansion CTE in the range from 0to 50° C. of not more than 0±0.1×10⁻⁶/K and thermal hysteresis at leastwithin the temperature range of 10-35° C. of <0.1 ppm and whichcomprises the following components (in mol % based on oxide):

SiO₂ 60-71  Li₂O 7-9.4 MgO + ZnO  0-<0.6

at least one component selected from the group consisting of P₂O₅, R₂O,where R₂O may be Na₂O and/or K₂O and/or Cs₂O and/or Rb₂O, and RO, whereRO may be CaO and/or BaO and/or SrO, and

nucleating agent in a content of 1.5 to 6 mol %, where nucleating agentis at least one component selected from the group consisting of TiO₂,ZrO₂, Ta₂O₅, Nb₂O₅, SnO₂, MoO₃, WO₃.

In a further aspect, the invention relates to the use of a glass ceramicaccording to the invention as substrate for a precision component.

In a further aspect, the invention relates to the use of an LAS glassceramic according to the invention in a precision component, especiallyfor use in metrology, spectroscopy, measurement technology, lithography,astronomy or observation of the Earth from space, for example as mirroror mirror substrate for segmented or monolithic astronomical telescopesor else as lightweight or ultralight mirror substrates, for example forspace-based telescopes or as high-precision structure components formeasurement of distance, for example in space, or optics for observationof the Earth, as precision components, such as standards for precisionmeasurement technology, precision measurement scales, reference platesin interferometers, as mechanical precision parts, for example for ringlaser gyroscopes, spiral springs for the clock industry, for example asmirrors and prisms in LCD lithography, and, for example, as maskholders, wafer stages, reference plates, reference frames and gridplates in microlithography and in EUV (extreme UV) microlithography, inwhich reflective optics are used, and additionally as mirrors and/orphotomask substrates or reticle mask blanks in EUV microlithography.

In another aspect, the invention relates to a precision componentcomprising an LAS glass ceramic according to the invention.

The figures show:

FIG. 1 shows CTE-T curves of materials known from the prior art thathave low thermal lengthwise expansion, for example for precisioncomponents.

FIG. 2 shows hysteresis characteristics of three glass ceramic samplesascertained by the same method, which is also used in the presentinvention. This figure comes from R. Jedamzik et al., “Modeling of thethermal expansion behavior of ZERODUR® at arbitrary temperatureprofiles”, Proc. SPIE Vol. 7739, 2010.

FIGS. 3 to 8 show hysteresis curves of known materials of glass ceramicswhich can be used for production of known precision components and whichhave thermal hysteresis at least within the temperature range of 10-35°C. of >0.1 ppm (dashed=cooling curve, dotted=heating curve).

FIG. 9 shows the hysteresis curve (dashed=cooling curve, dotted=heatingcurve) of a prior art glass ceramic which can be used for production ofa precision component and which has thermal hysteresis at least withinthe temperature range of 10-35° C. of <0.1 ppm, but the steepprogression of the curve shows that the glass ceramic does not have zeroexpansion.

FIGS. 10 and 11 show hysteresis curves of glass ceramics according tothe invention (compositions according to Ex. 6 and Ex. 7 in Table 1),each of which can be used for production of a precision componentaccording to the invention and which have thermal hysteresis at leastwithin the temperature range of 10-35° C. of <0.1 ppm (dashed=coolingcurve, dotted=heating curve).

FIGS. 12 and 13 show a normalized Δl/l₀−T curve (also called dl/l₀curves) of a glass ceramic according to the invention (compositionsaccording to Ex. 6 and Ex. 7 in Table 1) and reference lines forascertaining the index F as a measure of the flatness of the expansioncurve within the temperature range from 0° C. to 50° C.

FIGS. 14 to 17 show normalized Δl/l₀−T curves of known materials thatcan be used for production of known precision components and referencelines for ascertaining the index F as a measure of the flatness of theexpansion curve within the temperature ranges from −20° C. or −10° C. to70° C. or 80° C.

FIG. 18 shows normalized Δl/l₀−T curves of glass ceramics of FIGS. 12and 13 within the temperature range from −30° C. to +70° C.

FIG. 19 shows normalized Δl/l₀−T curves of known materials within thetemperature range from −30° C. to +70° C.

FIGS. 20 and 21 show that the CTE-T curves of glass ceramics of FIGS. 12and 13, which can be used for production of advantageous precisioncomponents, advantageously have a CTE plateau.

FIGS. 22 and 23 show slopes of CTE-T curves from FIGS. 24 and 25.

FIGS. 24 and 25 show different CTE progressions for two examples of theinvention, established by different ceramization parameters.

FIG. 26 shows the slope of CTE-T curve of a glass ceramic according tothe invention having a composition according to Ex. 17 in table 1.

FIG. 27 shows a normalized Δl/l₀−T curve of a glass ceramic according tothe invention (composition according to Ex. 17 in Table 1) and referencelines for ascertaining the alternative index f_((20;40)) as a measure ofthe flatness of the expansion curve within the temperature range from20° C. to 40° C.

FIG. 28 shows a normalized Δl/l₀−T curve of the glass ceramic of FIG. 13and reference lines for ascertaining the alternative index f_((0.10;30))as a measure of the flatness of the expansion curve within thetemperature range from −10° C. to 30° C.

FIG. 29 shows a normalized Δl/l₀−T curve of the glass ceramic of FIG. 13and reference lines for ascertaining the alternative index f_((20;70))as a measure of the flatness of the expansion curve within thetemperature range from 20° C. to 70° C.

FIG. 30 shows a normalized Δl/l₀−T curve of a glass ceramic according tothe invention (composition according to Ex. 14 in Table 1) and referencelines for ascertaining the alternative index f_((−10;30)) as a measureof the flatness of the expansion curve within the temperature range from−10° C. to 30° C.

The invention provides an LAS glass ceramic having an averagecoefficient of thermal expansion CTE in the range from 0 to 50° C. ofnot more than 0±0.1×10⁻⁶/K and thermal hysteresis at least within thetemperature range of 10° C.-35° C. of <0.1 ppm, and comprising thefollowing components (in mol % based on oxide):

SiO₂ 60-71  Li₂O 7-9.4 MgO + ZnO  0-<0.6

at least one component selected from the group consisting of P₂O₅, R₂O,where R₂O may be Na₂O and/or K₂O and/or Cs₂O and/or Rb₂O, and RO, whereRO may be CaO and/or BaO and/or SrO, and

nucleating agent in a content of 1.5 to 6 mol %, where nucleating agentis at least one component selected from the group consisting of TiO₂,ZrO₂, Ta₂O₅, Nb₂O₅, SnO₂, MoO₃, WO₃.

The invention for the first time provides an LAS glass ceramic (alsocalled glass ceramic hereinafter) that combines multiple relevantproperties: it has an average coefficient of thermal expansion CTE inthe range from 0 to 50° C. of not more than 0±0.1×10⁻⁶/K, i.e. has zeroexpansion. It also has thermal hysteresis of <0.1 ppm at least withinthe temperature range from 10° C. to 35° C. A material having such asmall hysteresis effect of <0.1 ppm within the temperature rangementioned is referred to hereinafter as “hysteresis-free”. Since theextent of hysteresis, as already mentioned above, depends on the rate oftemperature change used for ascertainment thereof, the statementsrelating to hysteresis in the context of the invention relate to aheating rate/cooling rate of 36 K/h, i.e. 0.6 K/min. In advantageousembodiments, the LAS glass ceramic may be hysteresis-free at leastwithin the temperature range of 5° C. to 35° C. or at least 5° C. to 40°C., advantageously at least within the temperature range of >0° C. to45° C., preferably at least within the temperature range of −5° C. to50° C.

The features of CTE and thermal hysteresis are described in detailfurther down.

A glass ceramic is understood in accordance with the invention to meaninorganic nonporous materials having a crystalline phase and a vitreousphase, with the matrix, i.e. the continuous phase, generally being aglass phase. For production of the glass ceramic, first of all, thecomponents of the glass ceramic are mixed, melted and refined, and whatis called a green glass is cast. The green glass, after cooling, iscrystallized in a controlled manner by reheating (called “controlledvolume crystallization”). The chemical composition (analysis) of thegreen glass and of the glass ceramic produced therefrom are the same;the ceramization alters exclusively the internal structure of thematerial. Therefore, if reference is made hereinafter to the compositionof the glass ceramic, the statements made are equally applicable to theprecursor article of the glass ceramic, i.e. the green glass.

The inventor has recognized that the two components MgO and ZnO promotethe occurrence of thermal hysteresis within the temperature rangeconsidered, and it is therefore essential for the provision of azero-expansion LAS glass ceramic which is hysteresis-free at leastwithin the temperature range of 10° C. to 35° C. to limit the content ofMgO and ZnO as specified in the claim. By contrast, it has been assumedto date that these glass components in combination or each individuallyare specifically necessary in zero-expansion LAS glass ceramics in orderto achieve zero expansion, and to make the shape of the CTE-T curve ofthe material “flat”, i.e. with a low slope of the CTE-T curve within therelevant temperature range. There was thus a conflict of objectives inthat an LAS glass ceramic could be either zero-expansion orhysteresis-free.

This conflict of objectives is resolved by the invention if not only theuse of MgO and ZnO is largely dispensed with, but the contents of SiO₂and Li₂O are additionally chosen from the ranges defined by theinvention. In the context of the invention, it has been found that,surprisingly, within the range defined by the contents for SiO₂ (60-71mol %) and for Li₂O (7-9.4 mol %), it is possible to obtainzero-expansion and hysteresis-free glass ceramics.

LAS glass ceramics contain a negatively expanding crystal phase which,in accordance with the invention, advantageously comprises or consistsof high quartz solid solution, also called β-eucryptite, and apositively expanding glass phase. As well as SiO₂ and Al₂O₃, Li₂O is amain constituent of the solid solution. If present, ZnO and/or MgO arelikewise incorporated into the solid solution phase, and together withLi₂O influence the expansion characteristics of the crystal phase. Thismeans that the abovementioned specifications according to the invention(reduction, preferably exclusion, of MgO and ZnO) have a significanteffect on the nature and properties of the solid solution formed in thecourse of ceramization. By contrast with the known zero-expansion glassceramics in which MgO and ZnO in particular are used for establishmentof the desired expansion characteristics of the glass ceramic, at leastone component selected from the group consisting of P₂O₅, R₂O, where R₂Omay be Na₂O and/or K₂O and/or Rb₂O and/or Cs₂O, and RO, where RO may beCaO and/or BaO and/or SrO, is used for this purpose in the context ofthe invention. Unlike MgO and ZnO, the alkaline earth metal oxides andalkali metal oxides mentioned, if present, however, remain in the glassphase and are not incorporated into the high quartz solid solution.

In the context of the invention, it has been found that it can beadvantageous for the provision of a zero-expansion and hysteresis-freeglass ceramic when the composition meets the condition that molarcontent of SiO₂+(5×molar content of Li₂O)≥106 or preferably 106.5,preferably molar content of SiO₂+(5×molar content of Li₂O)≥107 or≥107.5. Alternatively or additionally, in respect of the condition“molar content of SiO₂+(5×molar content of Li₂O)”, an advantageous upperlimit of ≤115.5 or of ≤114.5 or of ≤113.5 may be applicable.

In an advantageous development, the glass ceramic may comprise thefollowing components, individually or in any combination, in mol %:

Al₂O₃ 10 to 22 P₂O₅ 0 to 6 MgO   0 to 0.35 ZnO  0 to 0.5 R₂O 0 to 6 RO 0to 6 TiO₂ + ZrO₂ 1.5 to 6 

In an advantageous development, the glass ceramic may comprise thefollowing components, individually or in any combination, in mol %:

Al₂O₃ 10 to 22 P₂O₅ 0 to 6 MgO  0 to 0.3 ZnO  0 to 0.4 R₂O 0 to 6 RO 0to 6 TiO₂ + ZrO₂ 1.5 to 6 

Further preferably, the glass ceramic may include, within the scope ofthe abovementioned limits for the sums of R₂O, of RO and of TiO₂+ZrO₂,the following components individually or in any combination in mol %:

Na₂O 0 to 3 K₂O 0 to 3 Cs₂O 0 to 2 Rb₂O 0 to 2 CaO 0 to 5 BaO 0 to 4 SrO0 to 3 TiO₂ 0 to 5 ZrO₂ 0 to 3

In an advantageous embodiment, the LAS glass ceramic comprises (in mol %based on oxide):

Al₂O₃ 10 to 22 P₂O₅ 0 to 6 MgO   0 to 0.35 ZnO  0 to 0.5 R₂O 0 to 6 RO 0to 6 nucleating agent 1.5 to 6, 

where nucleating agent is preferably TiO₂ and/or ZrO₂.

In an advantageous embodiment, the LAS glass ceramic comprises (in mol %based on oxide):

Al₂O₃ 10 to 22 P₂O₅ 0 to 6 MgO  0 to 0.3 ZnO  0 to 0.4 R₂O 0 to 6 RO 0to 6 nucleating agent 1.5 to 6, 

where nucleating agent is preferably TiO₂ and/or ZrO₂.

In a further advantageous embodiment, the LAS glass ceramic comprises(in mol % based on oxide):

SiO₂ 60.50 to 69   Li₂O  8 to 9.4 Al₂O₃ 11 to 21 P₂O₅ 0.5 to 6  MgO  0to 0.2 ZnO  0 to 0.3 R₂O 0 to 4 RO 0.2 to 4.5 nucleating agent 2.5 to5, 

where nucleating agent is preferably TiO₂ and/or ZrO₂.

The glass ceramic contains a proportion of silicon dioxide (SiO₂) of atleast 60 mol %, more preferably at least 60.5 mol %, also preferably atleast 61 mol %, also preferably at least 61.5 mol %, further preferablyat least 62.0 mol %. The proportion of SiO₂ is at most 71 mol % or lessthan 71 mol %, more preferably at most 70 mol % or less than 70 mol %,further preferably at most 69 mol %, also preferably at most 68.5 mol %.In the case of greater proportions of SiO₂, the batch is more difficultto melt and the viscosity of the melt is higher, which can lead toproblems in the homogenization of the melts in industrial scaleproduction plants. Therefore, a content of 71 mol %, preferably 70 mol%, should not be exceeded. If the viscosity of a melt is high, there isan increase in the processing temperature Va of the melt. Very hightemperatures are required for the refining and homogenization of themelt, but these have the effect that the increasing aggressivity of themelt with temperature results in attack on the linings of the meltingequipment. Moreover, even higher temperatures may be insufficient toproduce a homogeneous melt, with the result that the green glass canhave streaks and inclusions (especially bubbles and particlesoriginating from the lining of the melting equipment), such that, afterthe ceramization, the demands on the homogeneity of the properties ofthe glass ceramic produced, for example the homogeneity of thecoefficient of thermal expansion, are not met. Lower SiO₂ contents thanthe upper limit mentioned may be preferable for that reason.

The proportion of Al₂O₃ is advantageously at least 10 mol %, preferablyat least 11 mol %, with preference at least 12 mol %, more preferably atleast 13 mol %, also preferably at least 14 mol %, also preferably atleast 14.5 mol %, further preferably at least 15 mol %. If the contentis too low, no solid solution is formed, or not enough solid solutionhaving low expansion is formed. The proportion of Al₂O₃ isadvantageously at most 22 mol %, preferably at most 21 mol %, withpreference at most 20 mol %, additionally preferably at most 19.0 mol %,more preferably at most 18.5 mol %. Too high an Al₂O₃ content leads toelevated viscosity and promotes the uncontrolled devitrification of thematerial.

The glass ceramic according to the invention may contain 0 to 6 mol % ofP₂O₅. The phosphate content P₂O₅ of the glass ceramic may advantageouslybe at least 0.1 mol %, preferably at least 0.3 mol %, with preference atleast 0.5 mol %, also preferably at least 0.6 mol %, more preferably atleast 0.7 mol %, further preferably at least 0.8 mol %. P₂O₅ isessentially incorporated into the crystal phase of the glass ceramic andhas a positive effect on the expansion characteristics of the crystalphase and hence of the glass ceramic. Moreover, melting of thecomponents and refining characteristics of the melt are improved. But iftoo much P₂O₅ is present, the progression of the CTE-T curve within thetemperature range of 0° C. to 50° C. does not show an advantageous flatprogression. Therefore, advantageously not more than 6 mol %, preferablynot more than 5 mol %, more preferably at most 4 mol %, furtherpreferably less than 4 mol %, of P₂O₅ may be present in the glassceramic. In individual embodiments, the glass ceramics may be free ofP₂O₅.

In the context of the invention, particular sums and ratios of thecomponents SiO₂, Al₂O₃ and/or P₂O₅, i.e. of the components that form thehigh quartz solid solution, may be beneficial for formation of a glassceramic according to the invention.

The cumulative proportion in mol % of the SiO₂ and Al₂O₃ baseconstituents of the LAS glass ceramic is advantageously at least 75 mol%, preferably at least 78 mol %, with preference at least 79 mol %, morepreferably at least 80 mol % and/or preferably at most 90 mol %,preferably at most 87 mol %, with preference at most 86 mol %, morepreferably at most 85 mol %. If this sum is too high, the viscositycurve of the melt is shifted to higher temperatures, which isdisadvantageous, as already elucidated above in connection with the SiO₂component. If the sum is too low, too little solid solution is formed.

The cumulative proportion in mol % of the SiO₂, Al₂O₃ and P₂O₅ baseconstituents of the LAS glass ceramic is preferably at least 77 mol %,advantageously at least 81 mol %, advantageously at least 83 mol %, morepreferably at least 84 mol % and/or preferably at most 91 mol %,advantageously at most 89 mol %, more preferably at most 87 mol %, andin one variant at most 86 mol %.

The ratio of the molar proportions of P₂O₅ to SiO₂ is preferably atleast 0.005, advantageously at least 0.01, with preference at least0.012 and/or preferably at most 0.1, more preferably at most 0.08, andin one variant at most 0.07.

As a further constituent, the glass ceramic contains lithium oxide(Li₂O) in a proportion of at least 7 mol %, advantageously at least 7.5mol %, preferably at least 8 mol %, especially preferably at least 8.25mol %. The proportion of Li₂O is limited to at most 9.4 mol %, morepreferably at most 9.35 mol %, additionally preferably at most or lessthan 9.3 mol %. Li₂O is a constituent of the solid solution phase andmakes an essential contribution to the thermal expansion of the glassceramic. Said upper limit of 9.4 mol % should not be exceeded since theresult is otherwise glass ceramics having a negative coefficient ofthermal expansion CTE (0;50). If the content of Li₂O is less than 7 mol%, too little solid solution is formed and the CTE of the glass ceramicremains positive.

The glass ceramic may contain at least one alkaline earth metal oxideselected from the group consisting of CaO, BaO, SrO, with this groupbeing referred to collectively as “RO”. The components from the RO groupremain essentially in the amorphous glass phase of the glass ceramic andmay be important for the preservation of zero expansion of the ceramizedmaterial. If the sum of CaO+BaO+SrO is too high, the target CTE (0;50)according to the invention is not attained. Therefore, the proportion ofRO is advantageously at most 6 mol % or at most 5.5 mol %, preferably atmost 5 mol %, advantageously at most 4.5 mol %, preferably at most 4 mol%, with preference at most 3.8 mol %, furthermore preferably at most 3.5mol %, also preferably at most 3.2 mol %. If the glass ceramic containsRO, an advantageous lower limit may be at least 0.1 mol %,advantageously at least 0.2 mol %, with preference at least 0.3 mol %,also preferably at least 0.4 mol %. In individual embodiments, the glassceramics may be free of RO.

The proportion of CaO may preferably be at most 5 mol %, advantageouslyat most 4 mol %, advantageously at most 3.5 mol %, advantageously atmost 3 mol %, further preferably at most 2.8 mol %, more preferably atmost 2.6 mol %. The glass ceramic may advantageously contain at least0.1 mol %, advantageously at least 0.2 mol %, preferably at least 0.4mol %, with preference at least 0.5 mol %, of CaO. The glass ceramic mayadvantageously contain the BaO component, which is a good glass former,in a proportion of at least 0.1 mol %, preferably at least 0.2 mol %and/or at most 4 mol %, advantageously at most 3 mol %, advantageouslyat most 2.5 mol %, preferably at most 2 mol %, with preference at most1.5 mol %, also preferably at most 1.4 mol %. The glass ceramic maycontain SrO in a proportion of at most 3 mol %, advantageously at most 2mol %, preferably at most 1.5 mol %, with preference at most 1.3 mol %,with preference at most 1.1 mol %, more preferably at most 1 mol %, alsopreferably at most 0.9 mol % and/or preferably at least 0.1 mol %. Inindividual embodiments, the glass ceramics are free of CaO and/or BaOand/or SrO.

Sodium oxide (Na₂O) and/or potassium oxide (K₂O) and/or caesium oxide(Cs₂O) and/or rubidium oxide (Rb₂O) are optionally present in the glassceramic, i.e. Na₂O-free and/or K₂O-free and/or Cs₂O-free and/orRb₂O-free variants are possible. The proportion of Na₂O mayadvantageously be at most 3 mol %, with preference at most 2 mol %,preferably at most 1.7 mol %, with preference at most 1.5 mol %, withpreference at most 1.3 mol %, with preference at most 1.1 mol %. Theproportion of K₂O may advantageously be at most 3 mol %, preferably atmost 2.5 mol %, with preference at most 2 mol %, with preference at most1.8 mol %, with preference at most 1.7 mol %. The proportion of Cs₂O mayadvantageously be at most 2 mol %, preferably at most 1.5 mol %, withpreference at most 1 mol %, with preference at most 0.6 mol %. Theproportion of Rb₂O may advantageously be at most 2 mol %, preferably atmost 1.5 mol %, with preference at most 1 mol %, with preference at most0.6 mol %. In individual embodiments, the glass ceramics are free ofNa₂O and/or K₂O and/or Cs₂O and/or Rb₂O.

Na₂O, K₂O, Cs₂O, Rb₂O may each independently be present in the glassceramic in a proportion of at least 0.1 mol %, preferably at least 0.2mol %, more preferably at least 0.5 mol %. The Na₂O, K₂O, Cs₂O and Rb₂Ocomponents remain essentially in the amorphous glass phase of the glassceramic and may be important for the preservation of the zero expansionof the ceramized material.

Therefore, the sum R₂O of the contents of Na₂O, K₂O, Cs₂O and Rb₂O mayadvantageously be at least 0.1 mol %, preferably at least 0.2 mol %,advantageously at least 0.3 mol %, with preference at least 0.4 mol %. Alow R₂O content of advantageously at least 0.2 mol % may contribute toincreasing the temperature range within which the expansion of the glassceramic shows a flat progression. The sum R₂O of the contents of Na₂O,K₂O, Cs₂O and Rb₂O may advantageously be at most 6 mol %, preferably atmost 5 mol %, with preference at most 4 mol %, with preference at most 3mol %, with preference at most 2.5 mol %. When the sum ofNa₂O+K₂O+Cs₂O+Rb₂O is too low or too high, it may be possible that thetarget CTE (0;50) according to the invention is not attained. Inindividual embodiments, the glass ceramics may be free of R₂O.

The glass ceramic may contain not more than 0.35 mol % of magnesiumoxide (MgO). A further advantageous upper limit may be not more than 0.3mol %, not more than 0.25 mol %, not more than 0.2 mol %, not more than0.15 mol %, not more than 0.1 mol % or not more than 0.05 mol %. Morepreferably, the glass ceramics according to the invention are free ofMgO. As already described above, the MgO component in the glass ceramiccauses thermal hysteresis within the temperature range from 0° C. to 50°C. The less MgO is present in the glass ceramic, the lower thehysteresis within the temperature range mentioned will be.

The glass ceramic may contain not more than 0.5 mol % of zinc oxide(ZnO). A further advantageous upper limit may be not more than 0.45 mol%, not more than 0.4 mol %, not more than 0.35 mol %, not more than 0.3mol %, not more than 0.25 mol %, not more than 0.2 mol %, not more than0.15 mol %, not more than 0.1 mol % or not more than 0.05 mol %. Morepreferably, the glass ceramics according to the invention are free ofZnO. As already described above as a finding by the inventor, the ZnOcomponent in the glass ceramic causes thermal hysteresis within thetemperature range from 0° C. to 50° C. The less ZnO is present in theglass ceramic, the lower the hysteresis within the temperature rangementioned will be.

With regard to the freedom from hysteresis of the glass ceramicaccording to the invention, it is important that the condition thatMgO+ZnO is less than 0.6 mol % is met. A further advantageous upperlimit of for the sum of MgO+ZnO may be not more than 0.55 mol %, notmore than or less than 0.5 mol %, not more than 0.45 mol %, not morethan 0.4 mol %, not more than 0.35 mol %, not more than 0.3 mol %, notmore than 0.25 mol %, not more than 0.2 mol %, not more than 0.15 mol %,not more than 0.1 mol % or not more than 0.05 mol %.

The glass ceramic also contains at least one crystal nucleating agentselected from the group consisting of TiO₂, ZrO₂ Ta₂O₅, Nb₂O₅, SnO₂,MoO₃, WO₃. Nucleating agents may be a combination of two or more of thecomponents mentioned. A further advantageous nucleating agent may beHfO₂. Therefore, in an advantageous embodiment the glass ceramiccomprises HfO₂ and at least one nucleating agent selected from the groupconsisting of TiO₂, ZrO₂ Ta₂O₅, Nb₂O₅, SnO₂, MoO₃, WO₃. The sum of theproportions of the nucleating agents is preferably at least 1.5 mol %,with preference at least 2 mol % or more than 2 mol %, more preferablyat least 2.5 mol %, and in particular variants at least 3 mol %. Anupper limit may be not more than 6 mol %, preferably not more than 5 mol%, with preference not more than 4.5 mol % or not more than 4 mol %. Inparticularly advantageous variants, the upper and lower limits mentionedare applicable to the sum of TiO₂ and ZrO₂.

The glass ceramic may contain titanium dioxide (TiO₂), preferably in aproportion of at least 0.1 mol %, advantageously at least 0.5 mol %,preferably at least 1.0 mol %, with preference at least 1.5 mol %, withpreference at least 1.8 mol % and/or preferably at most 5 mol %,advantageously at most 4 mol %, more preferably at most 3 mol %, furtherpreferably at most 2.5 mol %, with preference 2.3 mol %. TiO₂-freevariants of the glass ceramic according to the invention are possible.

The glass ceramic may advantageously further contain zirconium oxide(ZrO₂) in a proportion of at most 3 mol %, preferably at most 2.5 mol %,further preferably at most 2 mol %, with preference at most 1.5 mol % orat most 1.2 mol %. ZrO₂ may preferably be present in a proportion of atleast 0.1 mol %, more preferably at least 0.5 mol %, at least 0.8 mol %or at least 1.0 mol %. ZrO₂-free variants of the glass ceramic accordingto the invention are possible.

In some advantageous variants of the invention, individually or in sum,0 to 5 mol % of Ta₂O₅ and/or Nb₂O₅ and/or SnO₂ and/or MoO₃ and/or WO₃may be present in the glass ceramic and, for example, as an additionalor alternative nucleating agents or for modulation of the opticalproperties, for example refractive index. HfO₂ may likewise bealternative or additional nucleating agent. For modulation of theoptical properties, it is possible in some advantageous variants, forexample, for Gd₂O₃, Y₂O₃, HfO₂, Bi₂O₃ and/or GeO₂ to be present.

The glass ceramic may further comprise one or more usual refiningagents, selected from the group consisting of As₂O₃, Sb₂O₃, SnO₂, SO₄²⁻, F⁻, Cl⁻, Br⁻ or a combination therefrom, in an amount of more than0.05 mol % or at least 0.1 mol % and/or at most 1 mol %. The finingagent fluorine can lower the transparency of the glass ceramic, and sothis component, if it should be present, is preferably limited to notmore than 0.5 mol %, with preference not more than 0.3 mol %, withpreference not more than 0.1 mol %. The glass ceramic is preferably freeof fluorine.

The above glass compositions may optionally contain additions ofcolouring oxides, for example Nd₂O₃, Fe₂O₃, CoO, NiO, V₂O₅, MnO₂, CuO,CeO₂, Cr₂O₃, rare earth oxides, in contents, each individually or insum, of 0-3 mol %. Preferred variants are free of colouring oxides.

B₂O₃ can have an adverse effect on the transparency of the glassceramic. Therefore, the content of this component in an advantageousvariant is limited to <0.2 mol %, preferably at most 0.1 mol %.Preferred variants are free of B₂O₃.

In an advantageous embodiment of the present invention, the compositionis free of components that are not mentioned above.

In an advantageous embodiment of the present invention, the glassceramic according to the invention or the green glass consistspreferably to an extent of at least 90 mol %, more preferably to anextent of at least 95 mol %, most preferably to an extent of at least 99mol %, of the aforementioned components, and preferably of the SiO₂,Al₂O₃, Li₂O, P₂O₅, R₂O, RO and nucleating agent components.

In an advantageous development of the glass ceramic, the latter isessentially free of one or more glass components selected from the groupconsisting of MgO, ZnO, PbO, B₂O₃, CrO₃, F, Cd compounds.

According to the invention, what is meant by the expression “X-free” or“free of a component X” is that the glass ceramic essentially does notcontain this component X, meaning that such a component is present inthe glass as an impurity at most, but is not added to the composition asan individual component. With regard to any contamination, especiallywith MgO and/or ZnO, in the case of MgO-free and/or ZnO-free variants, alimit of 0.03 mol %, preferably 0.01 mol %, should not be exceeded,based on an individual component in each case. For other glasscomponents, higher impurity contents up to not more than 0.1 mol %,preferably not more than 0.05 mol %, advantageously not more than 0.01mol %, advantageously not more than 0.005 mol %, for some componentsadvantageously not more than 0.003 mol %, based on one component in eachcase, may be possible. X here represents any component, for example PbO.

The glass ceramics according to the invention have high quartz solidsolution as main crystal phase. The main crystal phase is thecrystalline phase having the greatest percentage by volume in thecrystal phase. High quartz solid solution is a metastable phase which,depending on the crystallization conditions, changes its compositionand/or structure or is transformed to a different crystal phase. Thehigh quartz-containing solid solutions have very low thermal expansion,or even falling thermal expansion with rising temperature. In anadvantageous execution, the crystal phase does not contain anyβ-spodumene or any keatite.

Advantageous executions of the LAS glass ceramic have a crystal phasecontent of less than 70% by volume and/or advantageously more than 45%by volume. The crystal phase consists of high quartz solid solution,which is also called β-eucryptite solid solution. The averagecrystallite size of the high quartz solid solution is advantageously<100 nm, preferably <80 nm, with preference <70 nm. The effect of thesmall crystallite size is that the glass ceramic is transparent and canalso be better polished. In some advantageous variants, the averagecrystallite size of the high quartz solid solution can be ≤60 nm,preferably ≤50 nm. The crystal phase, the proportion thereof and theaverage crystallite size are determined in a known manner by means ofx-ray diffraction analysis.

In one embodiment of the present invention, a transparent glass ceramicis produced. As a result of the transparency, it is possible to betterassess many properties of such a glass ceramic, especially of course theinternal quality thereof. The glass ceramics according to the inventionare transparent, meaning that they have an internal transmission of atleast 70% in the wavelength range from 350 to 650 nm. B₂O₃ and/or highercontents of fluorine can reduce transparency. Therefore, advantageousvariants do not contain one or both of the components mentioned.Moreover, the glass ceramics produced in the context of the inventionare free of pores and cracks. In the context of the invention, what ismeant by “pore-free” is a porosity of less than 1%, preferably less than0.5%, more preferably von less than 0.1%. A crack is a gap, i.e.discontinuity, in an otherwise continuous structure.

In order to enable the manufacture of a homogeneous glass ceramic inindustrial scale production plants, it is advantageous when theprocessing temperature Va of the parent green glass of the glass ceramic(and hence of the glass ceramic) is advantageously not more than 1330°C., preferably not more than 1320° C. Some advantageous variants mayhave a processing temperature of not more than 1310° C. or not more than1300° C. or less than 1300° C. The processing temperature Va is thetemperature at which the melt has a viscosity of 104 dPas. Homogeneityrelates especially to the homogeneity of the CTE of the glass ceramicover a large volume, and a small number, preferably freedom from,inclusions such as bubbles and particles. This is a quality feature ofthe glass ceramic and is a prerequisite for use in precision components,especially in very large precision components.

The processing temperature is determined by the composition of the glassceramic. Since the glass network-forming SiO₂ component in particular isregarded as a crucial component for increasing the viscosity and hencethe processing temperature, the maximum SiO₂ content should be chosen inaccordance with the above specifications.

CTE

The glass ceramics according to the invention have zero expansion (seeTable 1), meaning that they have an average coefficient of thermalexpansion CTE in the range from 0 to 50° C. of at most 0±0.1×10⁻⁶/K.Some advantageous variants even have an average CTE in the range from 0to 50° C. of at most 0±0.05×10⁻⁶/K. For particular applications, it maybe advantageous when the average CTE over a wider temperature range, forexample in the range from −30° C. to +70° C., preferably in the rangefrom −40° C. to +80° C., is at most 0±0.1×10⁻⁶/K, i.e. there is zeroexpansion.

For determination of the CTE-T curve of the glass ceramics and precisioncomponents according to the invention and of the comparative examples,the differential CTE(T) is first determined. The differential CTE(T) isdefined as a function of temperature. The CTE is then defined accordingto the following formula (1):

CTE(T)=(1/l ₀)×(∂I/∂T)  (1)

For creation of a Δl/l₀−T curve or an expansion curve or plot of thechange in length Δl/l₀ of a test specimen (glass ceramic or precisioncomponent) against temperature, it is possible to measure thetemperature-dependent change in length of the length of a test specimenfrom the starting length l₀ at the starting temperature t₀ to the lengthl_(t) at the temperature t. It is preferable here to choose smalltemperature intervals of, for example, 5° C. or 3° C. or 1° C. fordetermination of a measurement point. Such measurements may beconducted, for example, by dilatometry methods, interferometry methods,for example the Fabry-Perot method, i.e. the evaluation of the shift inthe resonance peak of a laser beam injected into the material, or othersuitable methods. In the context of the invention, the dilatometrymethod with a temperature interval of 1° C. on rod-shaped samples of thetest specimens with length 100 mm and diameter 6 mm was chosen toascertain the CTE. The chosen method of determining the CTE has anaccuracy of preferably at least ±0.05 ppm/K, with preference of at least±0.03 ppm/K. The CTE may of course also be determined by methods havingan accuracy of at least ±0.01 ppm/K, with preference at least ±0.005ppm/K or in some embodiments even of at least ±0.003 ppm/K or at least±0.001 ppm/K.

The Δl/l₀−T curve is used to calculate the average CTE for a particulartemperature interval, for example for the temperature range of 0° C. to50° C.

A CTE-T curve is determined via the derivative of the Δl/l₀−T curve. TheCTE-T curve can be used to determine the zero crossing, the slope of theCTE-T curve within a temperature interval. The CTE-T curve is used todetermine the shape and position of any advantageous CTE plateau formedin some variants (see below and FIGS. 20 and 21).

An advantageous embodiment of a precision component comprising a glassceramic according to the invention (especially in the form of asubstrate) has high CTE homogeneity. The value of CTE homogeneity(“total spatial variation of CTE”) is understood to mean what is calledthe peak-to-valley value, i.e. the difference between the respectivehighest and lowest CTE values of the samples taken from a precisioncomponent. CTE homogeneity is thus based not on the CTE of the materialof the component but on the spatial variation of the CTE over thesection under consideration or the entire precision component. Fordetermination of CTE homogeneity, a multitude of samples is taken fromdifferent sites in a precision component and the CTE value is determinedfor each, reported in ppb/K, where 1 ppb/K=0.001×10⁻⁶/K. CTEhomogeneity, i.e. the spatial variation of the CTE, over the entireprecision component, is advantageously at most 5 ppb/K, preferably atmost 4 ppb/K, most preferably at most 3 ppb/K. A method of ascertainingCTE homogeneity and measures for achieving CTE homogeneity are describedin WO 2015/124710 A, the disclosure-content of which is incorporatedinto this application in full.

Thermal Hysteresis

In the context of the invention, the glass ceramic, at least within thetemperature range of 10° C. to 35° C., has thermal hysteresis of <0.1ppm and is therefore hysteresis-free (see FIGS. 10 and 11). Thus, at anytemperature within the temperature interval of 10° C. to 35° C., theglass ceramic, once it has been subjected to a change in temperature,shows an isothermal change in length of less than 0.1 ppm at asubsequently constant temperature.

In advantageous embodiment, this freedom from hysteresis is preferablyat least within a temperature range from 5 to 35° C., preferably atleast within the temperature range from 5 to 45° C., preferably at leastwithin the temperature range from >0° C. to 45° C., with preference atleast within the temperature range from −5° C. to 50° C. Morepreferably, the temperature range for the freedom from hysteresis iseven broader, such that the material or component is also suitable forapplications at temperatures up to at least 100° C. and advantageouslyalso even higher. More preferably, the temperature range for the freedomfrom hysteresis is even broader. Preferred application temperatures arein the range of −60 to 100° C., more preferably of −40° C. to +80° C.Particular variants of the present invention relate to glass ceramicsand precision components for application temperatures T_(A), forexample, in the range of 5° C. to 20° C. or T_(A) of 22° C., 40° C., 60°C., 80° C. and 100° C., which are preferably hysteresis-free even atthese temperatures as well.

Thermal hysteresis was determined for the glass ceramics and precisioncomponents according to the invention and for the comparative examplesusing a precision dilatometer capable of ascertaining the CTE with areproducibility of ±0.001 ppm/K and ±0.003 ppm/K absolute, with atemperature interval of 1° C., on rod-shaped samples of length 100 mmand diameter 6 mm of the test specimens (i.e. sample of the precisioncomponent or sample of the glass ceramic), in accordance with the methodand apparatus construction disclosed in DE 10 2015 113 548 A, thedisclosure-content of which is incorporated into this application infull. For every sample examined, the change in length Δl/l₀ wasdetermined as a function of temperature between 50° C. to −10° C.,cooling at a cooling rate of 36 K/h. After an isothermal hold time of 5hours at −10° C., the sample was heated at a heating rate of 36 K/h to50° C., and the change in length Δl/l₀ was recorded as a function oftemperature. The thermal hysteresis characteristics of a test specimenare considered at −5° C., 0° C., 5° C., 10° C., 22° C., 35° C., 40° C.These points are representative of the temperature range from −10° C. to50° C., since hysteresis decreases with rising temperature within thetemperature interval mentioned. Thus, a sample which is hysteresis-freeat 22° C. or 35° C. also shows no hysteresis in the range up to 50° C.

For determination of thermal hysteresis at 10° C., the individualmeasurement values of the change in length for the five temperatures of8° C., 9° C., 10° C., 11° C. and 12° C., i.e. two temperature pointsabove and two temperature points below 10° C., were recorded both in thecourse of heating and in the course of cooling of the sample within therange of −10° C. to 50° C. at the rate of 36 K/h. The differencesbetween the measurement values for heating curve and cooling curve atthese five measurement points were used to form the average, which islisted in the tables as “Hyst.@10° C.” in the unit [ppm].

For determination of thermal hysteresis at 35° C., correspondingly, theindividual measurement values of change in length for the fivetemperatures 33° C., 34° C., 35° C., 36° C. and 37° C., i.e. twotemperature points above and two temperature points below 35° C., wererecorded both in the course of heating and in the course of cooling ofthe sample within the range of −10° C. to 50° C. at the rate of 36 K/h.The differences between the measurement values for heating curve andcooling curve of these five measurement points were used to form theaverage, which is listed in the tables as “Hyst.@35° C.” in the unit[ppm].

The corresponding procedure was followed for the other abovementionedtemperature points.

The FIGS. 2 to 11 show thermal hysteresis curves of glass ceramicsaccording to the invention (FIGS. 10 and 11) and of known glass ceramics(FIGS. 2 to 9). For better comparability, a range of 6 ppm was alwayschosen on the y axis for the representation in the figures.

FIGS. 2 to 8 show the thermal hysteresis curves of known materials thatare used for precision components. The cooling curves (dashed) andheating curves (dotted) are each clearly spaced apart from one anotherspecifically at lower temperatures, i.e. they have a distinctly separateprogression. At 10° C., the difference is more than 0.1 ppm, anddepending on the comparative example up to about 1 ppm. In other words,the materials and the precision components manufactured therefrom showconsiderable thermal hysteresis within the relevant temperature range ofat least 10 to 35° C.

The LAS glass ceramics examined that are shown in FIGS. 2 to 5(Comparative Examples 7, 9 and 10 in Table 2) all contain MgO and ZnOand have thermal hysteresis over wide ranges within the temperatureinterval of 10° C. to 35° C. FIGS. 6 and 7 show the hysteresis curves ofLAS glass ceramics (Comparative Examples 8 and 14 in Table 2) that areMgO-free but ZnO-containing. Both materials show significantlyincreasing thermal hysteresis below 15° C. FIG. 8 shows the hysteresiscurve of a LAS glass ceramic (Comparative Example 15 in Table 2) that isZnO-free but MgO-containing. This material likewise shows significantlyincreasing thermal hysteresis below 15° C. As apparent in FIG. 9, thisknown material (Comparative Example 1 in Table 2) does not have thermalhysteresis, but the steep curve progression shows that it is not azero-expansion material. The average CTE here is −0.24 ppm/K.

LAS glass ceramics and precision components according to the inventionhave a very low content of MgO and/or ZnO or are preferably free of MgOand ZnO. As apparent in FIGS. 10 and 11, the heating curves and coolingcurves are superposed at least within the temperature range of 10° C. to35° C., meaning that the glass ceramics are hysteresis-free. However,the materials are hysteresis-free not only within the range of 10° C. to35° C., but likewise at least within the range of 5 to 35° C. or 5 to45° C., preferably at least within the range of >0° C. to 45° C. Example7 from FIG. 11 is also hysteresis-free at least within the temperaturerange of −5° C. to 50° C.

Further Expansion Properties

Advantageous embodiments of the invention have further advantageousexpansion features:

For description of the expansion characteristics of a test specimen(glass ceramic or precision component), a TCL value is frequentlyreported, with TCL meaning “total change of length”. In the context ofthe invention, the TCL value is reported for the temperature range of 0°C. and 50° C. It is ascertained from the normalized Δl/l₀−T curve (alsodl/l₀−T curve in the figures) of the respective test specimen, with“normalized” meaning that the change in length at 0° C. is 0 ppm. TheΔl/l₀−T curve for the determination of TCL is created by the same methodas described above in connection with the determination of CTE in thecontext of the invention.

The TCL value is the distance between the highest dl/l₀ value and thelowest dl/l₀ value within this temperature range:

TCL(0;50° C.)=|dl/l ₀ max.|+|dl/l ₀ min.|  (2)

where “dl” denotes the change in length at the respective temperatureand “l₀” the length of the test specimen at 0° C. The calculation isbased in each case on the absolute values of the dl/l₀ values.

FIGS. 14 to 17 show expansion curves of known materials, from which thedl/l₀ max. values and dl/l₀ min. values can each be read off forcalculation of the TCL value (see also below). The expansion curves eachshow a curved progression within the temperature range of 0° C. to 50°C.

In the context of the present invention, by contrast, a flat progressionof the expansion curves within the temperature range of 0° C. to 50° C.is an advantageous feature of the glass ceramic and of a precisioncomponent (see FIGS. 12 and 13). For some advantageous variants,depending on the field of use of the component, a flat progression ofthe expansion curve may also be desirable for another temperature range,especially within a range of (20;40), (20;70) and/or (−10;30).

As a statement as to the extent to which the curved progression of thethermal expansion differs from a simple linear progression, for anadvantageous embodiment of the invention, the index F is introduced as ameasure of the flatness of the expansion curve, which enables aclassification of CTE curves:

F=TCL(0;50° C.)/|expansion(0;50° C.)|  (3)

The index F is calculated by forming the quotient of the TCL (0;50)value [in ppm] (see above) and the difference in expansion between thetemperature points of 0° C. and 50° C. [in ppm]. Since the expansioncurve for the determination of TCL is normalized by definitions suchthat the change in length at 0° C. is 0 ppm, the “difference inexpansion between the temperature points of 0° C. and 50° C.”corresponds to the “expansion at 50° C.”, as stated in the tables. Theindex F is calculated using the absolute value of the expansion at 50°C.

It is advantageous here when the index F for the respective material orcomponent is <1.2, preferably <1.1, with preference at most 1.05. Thecloser the index F is to 1, the flatter the expansion curve.

It is apparent in FIGS. 12, 13 and 18 that advantageous embodiments ofthe LAS glass ceramic have a flat progression of the expansion curve(here F=1) within the temperature range of 0° C. to 50° C. andpreferably also within the broader temperature range of −30° C. to 70°C. By comparison, FIGS. 14 to 17 and 19 show that known materials show asignificantly steeper and more curved progression of the expansioncurves within the considered temperature ranges.

FIG. 12 shows, by way of example, the expansion curve of an advantageousglass ceramic with reference to an advantageous ceramization of Example6 composition. For the representation, a section of 1.6 ppm on the yaxis was chosen. The highest expansion value (dl/l₀ max.) is at +50° C.(dl/l₀ is +0.57 ppm, i.e. |0.57 ppm|); the lowest expansion value (dl/l₀min.) is 0 ppm. The difference in expansion between the temperaturepoints of 0° C. and 50° C., corresponding to the absolute value of the“expansion at 50° C.” is 0.57 ppm. This is used to calculate the index Ffor this material as follows: F (Example 7 from Table 1)=0.57 ppm/0.57ppm=1.

FIG. 13 shows a further advantageous example (composition according toExample 7 from Table 1) also having an Index F of 1.

Advantageous glass ceramics and precision components of the inventionthus have, for example within the temperature range from 0° C. to 50°C., a very flat progression of their expansion curves, meaning that theynot only have zero expansion in the considered temperature range butalso have a low variation in the change in linear expansion and hence inthe differential CTE within this range. As apparent in FIG. 18,advantageous examples of the invention also have a flat progression oftheir expansion curves over an even broader temperature range (here byway of example from −30° C. to +70° C.). By comparison, see thesignificantly steeper progressions of the expansion curves of knownmaterials based on the same temperature range in FIG. 19. The expansioncharacteristics can also be observed in other selected temperatureranges, especially (−10;30), (20;40), (20;70), which is describedfurther down.

By comparison with the advantageous embodiments of the glass ceramicsand precision components, FIGS. 14 to 17 show the expansioncharacteristics of known materials and precision components manufacturedtherefrom, from each of which the index F can be calculated. Theexpansion characteristics of the materials or precision components, asshown in FIGS. 14 to 17 and 19, were ascertained with the samedilatometer under comparable conditions as the expansion characteristicsof the advantageous embodiments of the glass ceramics shown in FIGS. 12,13 and 18. Overall, the known materials show a curved progression of theexpansion curves.

FIG. 14 shows the expansion curve of a commercially availabletitanium-doped quartz glass. As is apparent, the sum of the absolutevalues of the expansion value here at +50° C. (dl/l₀ max. is +0.73 ppm,i.e. |0.73 ppm|) and the expansion value at 14° C. (dl/l₀ min. is −0.19ppm, i.e. |0.19 ppm|) give a TCL(0;50) value of around 0.92 ppm. Thedifference in expansion between the temperature points of 0° C. and 50°C., corresponding to the absolute value of the “expansion at 50° C.”, is0.73 ppm. These are used to calculate the index F for this material asfollows: F (titanium-doped SiO₂)=0.92 ppm/0.73 ppm=1.26.

The index F is calculated correspondingly for a known LAS glass ceramicor for a corresponding precision component (see FIG. 15) as follows: F(known LAS glass ceramic)=1.19 ppm/0.11 ppm=10.82.

The index F is calculated correspondingly for a known cordierite glassceramic or a corresponding precision component (see FIG. 16) as follows:F (known cordierite glass ceramic)=2.25 ppm/0.25 ppm=9.

The index F is calculated correspondingly for a known sinteredcordierite ceramic or a corresponding precision component (see FIG. 17)as follows: F (known sintered cordierite ceramic)=4.2 ppm/2.71 ppm=1.55.

Glass ceramics having a flat progression of the expansion curves arevery advantageous since it is then possible not just to optimize aprecision component for the later application temperature, but also forit to have likewise low thermal expansion, for example, under higherand/or lower thermal loads, for example during production. Precisioncomponents for microlithography, EUV microlithography (also “EUVlithography” or “EUVL” for short) and metrology are typically used understandard cleanroom conditions, especially a room temperature of 22° C.The CTE may be matched to this application temperature. However, suchcomponents are subjected to various process steps, for example coatingwith metallic layers, or cleaning, structuring and/or exposureprocesses, in which temperatures may be higher or in some cases lowerthan those that prevail in the later use in a cleanroom. Advantageousglass ceramics and precision components manufactured therefrom that havean index F of <1.2 and hence optimized zero expansion not just atapplication temperature but also at possibly higher and/or lowertemperatures in production are thus very advantageous. Properties suchas freedom from hysteresis and an index F<1.2 are particularlyadvantageous if the precision component or a glass ceramic is used inEUV lithography, i.e. if, for example, the precision component is a EUVLmirror or EUVL mask blank or a corresponding substrate therefor, sinceparticularly the mirrors or masks in EUV lithography are heated by theirradiation with high-energy radiation in a very inhomogeneous mannerlocally or in beam direction. For such use conditions, it isadvantageous when the precision component or glass ceramic has a lowslope of the CTE-T curve within a temperature range around theapplication temperature (see below).

It is a feature of advantageous glass ceramics and precision componentsthat are even better optimized to a later application temperature at 20or 22° C. that they have a relative change in length (dl/l₀) of ≤|0.10|ppm, preferably of ≤|0.09| ppm, particularly preferably of ≤|0.08| ppmand especially preferably of ≤|0.07| ppm within the temperature rangefrom 20° C. to 30° C. and/or a relative change in length (dl/l₀) of≤|0.17| ppm, preferably of ≤|0.15| ppm, particularly preferably of≤|0.13| ppm and especially preferably of ≤|0.11| ppm within thetemperature range from 20° C. to 35° C. Alternatively or additionally,it may be a feature of such optimized glass ceramics and precisioncomponents that they have a relative change in length (dl/l₀) of ≤|0.30|ppm, preferably of ≤|0.25| ppm, particularly preferably of ≤|0.20| ppmand especially preferably of ≤|0.15| ppm within the temperature rangefrom 20° C. to 40° C. The features relating to the relative change inlength based on the different temperature intervals may preferably beinferred from the dl/l₀ curves of FIGS. 12 to 19. Of course, a statementof relative change of length (dl/l₀) relates to the absolute value ofthe respective value.

A zero-expansion, hysteresis-free material having such advantageousexpansion characteristics is particularly suitable for use as asubstrate for an EUVL mirror or as an EUVL mirror which is heated up todifferent degrees in operation, for example as a result of therespective exposure mask, in regions of light and shadow. On account ofthe abovementioned low relative change in length, an EUVL mirror formedfrom the advantageous glass ceramic has lower local gradients (or localslopes) in the topography of the mirror surface than an EUVL mirrormanufactured with known materials. The same is analogously applicable toEUVL mask blanks or EUVL masks or EUVL photomasks.

Especially in the case of a glass ceramic that shows a very flatprogression of the expansion curve within the considered temperaturerange that is close to 0 ppm or fluctuates around 0 ppm—whichconstitutes advantageous expansion characteristics overall—it may beadvantageous, alternatively or additionally to the index F, to introducea further measure of the flatness of the expansion curve in which theexpansion curve is considered not in the temperature range of (0;50) butwithin a different temperature interval (T.i.), preferably within thetemperature range of (20;40), (20;70) and/or (−10; 30). This enables theclassification of the expansion characteristics in relation to the laterfields of use.

The alternative index f_(T.i.) has the unit (ppm/K) and is defined as:

f _(T.i.) =TCL _((T.i.))/width of the temperature interval(T.i.)  (4)

where T.i. describes the considered temperature interval in each case.

The TCL_((T.i.)) value is the distance between the highest dl/l₀ valueand the lowest dl/l₀ value within the considered temperature range(T.i.) in each case, where the expansion curve for the determination ofthe TCL_((T.i.)) is also normalized by definition such that the changein length is 0 ppm at 0° C. In other words, for example:

TCL _((20;40° C.)) =|dl/l ₀ max.|+|dl/l ₀ min.|  (5)

where “dl” denotes the change in length at the particular temperatureand “l₀” the length of the test specimen at 0° C. The calculation isbased in each case on the absolute values of the dl/l₀ values.

The alternative index f_(T.i.) is calculated according to (4) by formingthe quotient from the TCL_((T.i.)) value [in ppm] (see above) and thewidth of the temperature interval (T.i.) reported in [K] in which thedifference in expansion is being considered. The width of thetemperature interval considered between 20° C. and 40° C. is 20 K. If,by contrast, the progression of the expansion curve is considered withinthe interval T.i.=(20;70) or (−10;30), the divisor for formula (4) is 50K and 40 K respectively.

In an advantageous embodiment the glass ceramic has an alternative indexf_((20;40))<0.024 ppm/K and/or an alternative index f_((20;70))<0.039ppm/K and/or an alternative index f_((−10;30))<0.015 ppm/K.

Glass ceramics having a very flat progression of the expansion curvesare very advantageous since it is then possible to optimize a precisioncomponent not just for the later application temperature but also, forexample, for higher and/or lower thermal loads that can be expected. Thealternative index f_(T.i.) is suitable for defining a suitable materialin accordance with the specifications required for particular componentapplications and for providing a corresponding precision component.Specific precision components and the uses thereof are described furtherdown and are hereby incorporated as well.

In an advantageous embodiment of the glass ceramic or a componentproduced therefrom, it may be advantageous when the alternative indexf_((20;40)) is <0.024 ppm/K, preferably <0.020 ppm/K, preferably <0.015ppm/K. A hysteresis-free, zero-expansion component having such expansioncharacteristics in the temperature range of (20;40) has particularlygood usability as precision component for microlithography and EUVmicrolithography at room temperature. An example of such advantageousglass ceramic is shown in FIG. 27.

In an advantageous embodiment of the glass ceramic or a componentproduced therefrom, it may be advantageous when the alternative indexf_((20;70)) is <0.039 ppm/K, preferably <0.035 ppm/K, preferably <0.030ppm/K, preferably <0.025 ppm/K, preferably <0.020 ppm/K. Ahysteresis-free, zero-expansion component having such expansioncharacteristics within the temperature range of (20;70) likewise hasparticularly good usability as precision component for microlithographyand EUV microlithography. It is particularly advantageous when thecomponent likewise has low thermal expansion even under high thermalloads that can occur, for example, during the production of theprecision component, but also locally or over an area in operation.Further details of the thermal loads that occur in the EUVL precisioncomponents have already been described above in connection with theindex F, to which reference is made here for avoidance of repetitions.One example of such an advantageous glass ceramic is shown in FIG. 29.

In an advantageous embodiment of the glass ceramic or a componentproduced therefrom, it may be advantageous when the alternative indexf_((−10;30)) is <0.015 ppm/K, preferably <0.013 ppm/K, preferably <0.011ppm/K. A hysteresis-free, zero-expansion component having such expansioncharacteristics in the temperature range of (−10;30) has particularlygood usability as precision component, especially as mirror substratesfor applications in which even lower temperatures than room temperaturecan occur, for example as mirror substrates in astronomy or observationof the Earth from space. Corresponding components are described furtherdown. Examples of such an advantageous glass ceramics are shown in FIGS.28 and 30.

A particularly advantageous embodiment of a glass ceramic or a componentproduced therefrom has an expansion curve for which at least 2 of thealternative indices f_((T.i.)) are applicable.

A particularly advantageous embodiment of a glass ceramic or a componentproduced therefrom has an expansion curve for which Index F and at leastone of the alternative indices f_((T.i.)) are applicable.

FIGS. 20 and 21 show that advantageous embodiments of the LAS glassceramic and of the precision component have a CTE plateau. A glassceramic having a plateau, i.e. having optimized zero expansion over abroad temperature range, offers the same advantages that have alreadybeen described above in connection with the flat progression of theexpansion curves and the index F.

It is advantageous when the differential CTE has a plateau close to 0ppm/K, meaning that the differential CTE within a temperature intervalT_(P) having a width of at least 40 K, preferably at least 50 K, is lessthan 0±0.025 ppm/K. The temperature interval of the CTE plateau isdefined as T_(P). Advantageously, the differential CTE within atemperature interval T_(P) having a range of at least 40 K may be lessthan 0±0.015 ppm/K.

A CTE plateau is thus understood to mean a range extending over asection of the CTE-T curve in which the differential CTE does not exceeda value of 0±0.025 ppm/K, preferably 0±0.015 ppm/K, more preferably0±0.010 ppm/K, further preferably 0±0.005 ppm/K, i.e. a CTE close to 0ppb/K.

Advantageously, the differential CTE within a temperature interval T_(P)having a width of at least 40 K is less than 0±0.015 ppm/K, i.e. 0±15ppb/K. In a preferred embodiment, a CTE plateau of 0±0.01 ppm/K, i.e.0±10 ppb/K, may be formed over a temperature interval of at least 50 K.In FIG. 25 the middle curve shows a CTE plateau of 0±0.005 ppm/K, i.e.0±5 ppb/K, between 7° C. and 50° C., i.e. over a width of more than 40K.

It may be advantageous when the temperature interval T_(P) is within arange from −10 to +100° C., preferably 0 to 80° C.

The position of the CTE plateau of the glass ceramic is preferablymatched to the application temperature T_(A) of the precision component.Preferred application temperatures T_(A) are in the range of −60° C. to+100° C., more preferably of −40° C. to +80° C. Particular variants ofthe present invention relate to precision components and glass ceramicsfor application temperatures T_(A) of 0° C., 5° C., 10° C., 22° C., 40°C., 60° C., 80° C. and 100° C. The CTE plateau, i.e. the curve regionhaving the low variance of the differential CTE within the temperatureinterval T_(P), may also be within the temperature range of [−10;100];[0;80], [0; 30° C.], [10; 40° C.], [20; 50° C.], [30; 60° C.], [40; 70°C.] and/or [50; 80° C.].

In an advantageous embodiment of the invention, the CTE-T curve of theglass ceramic or precision component within a temperature intervalhaving at least a width of 30 K, preferably at least a width of 40 K,more preferably at least a width of 50 K, has at least one curve-sectionwith low slope, especially a slope of at most 0±2.5 ppb/K²,advantageously of at most 0±2 ppb/K², advantageously of at most 0±1.5ppb/K², preferably of at most 0±1 ppb/K², preferably of at most 0±0.8ppb/K², and in specific variants even of at most 0±0.5 ppb/K².

The temperature interval with low slope is preferably matched to theapplication temperature T_(A) of the precision component. Preferredapplication temperatures T_(A) are in the range of −60° C. to +100° C.,more preferably from −40° C. to +80° C. Particular variants of thepresent invention relate to glass ceramics and precision components forapplication temperatures T_(A of) 0° C., 5° C., 10° C., 22° C., 40° C.,60° C., 80° C. and 100° C. The temperature interval with low slope mayalso be within the temperature range of [−10;100]; [0;80], [0; 30° C.],[10; 40° C.], [20; 50° C.], [30; 60° C.], [40; 70° C.] and/or [50; 80°C.].

FIG. 22 shows the slope of a CTE-T curve within the temperature rangefrom 0° C. to 45° C. for an advantageous glass ceramic or precisioncomponent using the composition of Example 6 from Table 1. The CTE slopeover the entire temperature range is below 0±2.5 ppb/K², and in aninterval ranging over at least 30 K even below 0±1.5 ppb/K².

In FIG. 23, it is apparent that the CTE slope of an advantageous glassceramic and precision component corresponding to composition of Example7 from Table 1 over the entire temperature range from 0° C. to 40° C.with a width of at least 40 K is below 0±1.0 ppb/K², and in an intervalranging over at least 30 K even below 0±0.5 ppb/K².

In FIG. 26, it is apparent that the CTE slope of an advantageous glassceramic and precision component corresponding to Example 17 from Table 1over the entire temperature range from 0° C. to 45° C. with a width ofat least 45 K is below 0±1.0 ppb/K², and in an interval ranging over atleast 30 K even below 0±0.5 ppb/K².

Glass ceramics and precision components having such expansioncharacteristics are of particularly good suitability for EUV lithographyapplications (for example as mirror or substrates for mirrors or masksor mask blanks), since the demands on the materials and precisioncomponents used for the optical components in this sector are becomingever higher with regard to extremely low thermal expansion, a zerocrossing of the CTE-T curve close to the application temperature and, inparticular, on a low slope of the CTE-T curve. In the context of theinvention, advantageous embodiments of a glass ceramic or precisioncomponent have a very flat CTE progression, with the progression showingboth a zero crossing and a very low CTE slope, and possibly a very flatplateau.

The feature of low slope may exist with or without formation of anadvantageous CTE plateau.

FIGS. 24 and 25 show how variation of ceramization temperature and/orceramization time can be used to adjust the CTE progression to differentapplication temperatures. As can be seen in FIG. 24, the zero crossingof the CTE-T curve at for example 12° C. can be moved to a value of 22°C. by means of increasing the ceramization temperature by 10 K. As analternative to an increase in the ceramization temperature, it is alsopossible to correspondingly prolong the ceramization time. FIG. 25exemplarily shows that the very flat progression of the CTE-T curve canbe raised—for example—by increasing the ceramization temperature by 5 or10 K. As an alternative to an increase in the ceramization temperature,it is also possible to correspondingly prolong the ceramization time.

Advantageous glass ceramics and precision components also have goodinternal quality. They preferably have at most 5 inclusions per 100 cm³,more preferably at most 3 inclusions per 100 cm³, most preferably atmost 1 inclusion per 100 cm³. Inclusions are understood in accordancewith the invention to mean both bubbles and crystallites having adiameter of more than 0.3 mm.

In one variant of the invention, precision components having a diameteror edge length of at most 800 mm and a thickness of at most 100 mm andhaving at most 5, preferably at most 3, more preferably at most 1,inclusion(s) for each 100 cm³ with a diameter of a size of more than0.03 mm are provided.

As well as the number of inclusions, the maximum diameter of theinclusions detected also serves as a measure of the level of internalquality. The maximum diameter of individual inclusions in the totalvolume of a precision component having a diameter of less than 500 mm ispreferably at most 0.6 mm, and in the critical volume for theapplication, for example close to the surface, preferably at most 0.4mm. The maximum diameter of individual inclusions in glass ceramiccomponents having a diameter of 500 mm to less than 2 m is preferably atmost 3 mm, and in the critical volume for the application, for exampleclose to the surface, preferably at most 1 mm.

The invention further relates to the use of a glass ceramic according tothe invention in a precision component. The glass ceramic may, forexample, form a substrate for the precision component.

The invention further relates to the use of an LAS glass ceramicaccording to the invention in a precision component, especially for usein metrology, spectroscopy, measurement technology, lithography,astronomy or observation of the Earth from space, for example as mirroror mirror substrate for segmented or monolithic astronomical telescopesor else as lightweight or ultralight mirror substrates, for example forspace-based telescopes or as high-precision structure components formeasurement of distance, for example in space, or optics for observationof the Earth, as precision components, such as standards for precisionmeasurement technology, precision measurement scales, reference platesin interferometers, as mechanical precision parts, for example for ringlaser gyroscopes, spiral springs for the clock industry, for example asmirrors and prisms in LCD lithography, and, for example, as maskholders, wafer stages, reference plates, reference frames and gridplates in microlithography and in EUV (extreme UV) microlithography, andadditionally as mirrors or mirror substrates and/or photomask substratesor photomask blanks or reticle mask blanks in EUV microlithography.

A glass ceramic according to the invention can be used to produceprecision components of different sizes:

One embodiment relates to precision components having relatively lowdimensions, especially in the case of (rect)angular shapes having alength (with and/or depth) or in the case of round areas havingdiameters of at least 100 mm and/or not more than 1500 mm and/or athickness of less than 50 mm, preferably less than 10 mm and/or at least1 mm, more preferably at least 2 mm. Such precision components can beemployed, for example, in microlithography and EUV lithography.

Another embodiment relates to precision components having very smalldimensions, especially having edge lengths (with and/or depth) ordiameters and/or thickness of a few mm (for example at most 20 mm or atmost 10 mm or at most 5 mm or at most 2 mm or at most 1 mm) to a fewtenths of a mm (for example at most 0.7 mm or at most 0.5 mm). Theseprecision elements may, for example, be a spacer, for example in aninterferometer, or a component for ultrastable clocks in quantumtechnology.

It is alternatively possible to produce very large precision components.One embodiment of the invention thus relates to components of largervolume. In the context of this application, this shall be understood tomean a component having a mass of at least 300 kg, preferably at least400 kg, preferably at least 500 kg, preferably at least 1 t, morepreferably at least 2 t, and in one variant of the invention at least 5t, or having edge lengths (with and/or depth) in the case of(rect)angular shapes of at least 0.5 m, more preferably at least 1 m,and a thickness (height) of at least 50 mm, preferably at least 100 mm,or in the case of round shapes having a diameter of at least 0.5 m, morepreferably at least 1 m, more preferably at least 1.5 m, and/or having athickness (height) of at least 50 mm, preferably at least 100 mm. Inspecific embodiments of the invention, the components may be even largerwith, for example, a diameter of at least 3 m or at least 4 m or larger.In one variant, the invention also relates to rectangular components,with at least one surface preferably having an area of at least 1 m²,preferably at least 1.2 m², more preferably at least 1.4 m². In general,large-volume components having a distinctly greater base area thanheight are produced. However, components may also be large-volumecomponents having a shape approximating to a cube or sphere.

Precision components may, for example, be optical components,specifically what is called a normal-incidence mirror, i.e. a mirrorwhich is operated close to the perpendicular angle of incidence, or whatis called a grazing-incidence mirror, i.e. a mirror which is operated ata grazing angle of incidence. Such a mirror comprises, as well as thesubstrate, a coating that reflects the instant radiation. Especially inthe case of a mirror or x-radiation, the reflective coating is, forexample, a multilayer system having a multitude of layers having highreflectivity in the x-ray range in the case of non-grazing incidence.Preferably, such a multilayer system of a normal-incidence mirrorcomprises 40 to 200 pairs of layers, consisting of alternating layers,for example of one of the material pairs Mo/Si, Mo/Bi, Ru/Si and/orMoRu/Be.

In particular, the optical elements according to the invention may bex-ray-optical elements, i.e. optical elements that are used inconjunction with x-radiation, especially soft x-radiation or EUVradiation, especially reticle masks or photomasks operated inreflection, especially for EUV microlithography. These mayadvantageously be mask blanks. Further advantageously, the precisioncomponent is usable as a mirror for EUV lithography or as a substratefor a mirror for EUV lithography.

In addition, the precision component of the invention may be acomponent, especially a mirror, for astronomy applications. Suchcomponents for use in astronomy may be used either terrestrially or inspace. High-precision structure components for measurement of distance,for example in space, are a further advantageous field of use.

The precision component of the invention may be a lightweight structure.The component of the invention may also comprise a lightweightstructure. This means that, in some regions of the component, cavitiesare provided for lightening the weight. The weight of a component ispreferably reduced by lightweight processing by at least 80%, morepreferably at least 90%, compared to the unprocessed component.

The invention further provides a precision component comprising an LASglass ceramic according to the invention. Details in this regard havealready been described above in connection with the glass ceramic anduse thereof in precision components. This disclosure is fullyincorporated into the description of the precision component.

It will be apparent that the features of the invention mentioned aboveand still to be elucidated hereinafter are usable not just in theparticular combination specified but also in other combinations withoutleaving the scope of the invention.

EXAMPLES

Tables 1 and 2 show compositions of examples of glass ceramics accordingto the invention and compositions of comparative examples, and theproperties thereof.

The compositions given in Table 1 were melted from commercial rawmaterials, such as oxides, carbonates and nitrates in customaryproduction processes. The green glasses produced according to Table 1were ceramized at the maximum temperatures specified over the timespecified.

The production of a glass ceramic for a precision component, especiallya large precision component, is described, for example, in WO2015/124710 A1.

Table 1 shows 23 examples (Ex.) of the invention which arehysteresis-free at least within a temperature range of 10° C. to 35° C.and have zero expansion. Examples 6, 18, 19 und 20 show incipientthermal hysteresis only from about 0° C., Examples 11, 17 and 23 onlyfrom about −5° C. Examples 7, 12, 14, 15 and 22 are hysteresis-free overthe entire temperature range from −5° C. to 45° C. Moreover, the index Fis <1.2, i.e. the progression of the expansion curve within thetemperature range of 0° C. to 50° C., is advantageously flat for allexamples. In addition, the examples have a processing temperature of≤1330° C., such that the glass ceramics can be produced with highhomogeneity in industrial scale production plants. The processingtemperatures as reported in Tables 1 and 2 were ascertained according toDIN ISO 7884-1 (2014—source: Schott Techn. Glas-Katalog).

In the case of Example 5, after ceramization at not more than 780° C.over a period of 2.5 days, the average CTE was determined for furthertemperature intervals with the following result: CTE (20; 300° C.):−0.17 ppm/K, CTE (20; 500° C.): −0.02 ppm/K, CTE (20; 700° C.): 0.17ppm/K.

For Example 7, the average CTE was determined for the temperature rangeof 19° C. to 25° C., with the result that Example 7 has a CTE (19;25) of−1.7 ppb/K.

Table 2 shows comparative examples (Comp. Ex.). Comparative Examples 1,2, 5 and 6 include neither MgO nor ZnO, but the average CTE(0;50) isgreater than 0±0.1×10⁻⁶/K, i.e. these comparative examples do not havezero expansion. In addition, Comparative Examples 1 and 2 have aprocessing temperature of >1330° C. These materials are very viscous,and so it is not possible to use these to manufacture components havinghigh homogeneity in industrial scale production plants.

Comparative Examples 7 to 16 all contain MgO and/or ZnO, and most ofthem have zero expansion. However, these comparative examples, at leastwithin the temperature range of 10° C. to 35° C., show thermalhysteresis of significantly more than 0.1 ppm. At room temperature, i.e.22° C., this group of comparative examples has thermal hysteresis apartfrom Comparative Examples 14 and 16. Comparative Example 9, even thoughit has zero expansion, also has a disadvantageously steep progression ofthe expansion curve in the temperature range of 0° C. to 50° C., whichis apparent from the high value of the index F.

Empty fields in the tables below in the figures for the composition meanthat this/these component(s) was/were not added deliberately or is/arenot present.

Table 3 shows, for some advantageous examples of the invention and onecomparative example, the alternative index f_((T.i.)) calculated fordifferent temperature intervals, from which it is apparent that theexpansion curves of the examples within the temperature ranges definedeach have a flatter progression than the comparative example.

It will be clear to a person skilled in the art that—depending on theapplication temperature of the glass ceramic or precision componentcomprising the glass ceramic—a glass ceramic having the desiredproperties, especially with regard to thermal hysteresis and/or averageCTE, is being chosen.

TABLE 1 Composition, ceramization and properties (mol %) Example No.(Ex.) 1 2 3 4 5 6 Li₂O 8.5 8.6 8.65 8.75 9.0 8.7 Na₂O 0.6 0.5 0.5 0.40.2 K₂O 1.65 1.6 1.65 1.45 0.75 0.6 MgO ZnO CaO 0.45 0.7 1.2 1.6 2.12.35 BaO 0.4 0.4 0.75 SrO Al₂O₃ 16.1 15.2 16.65 17.55 15.85 16.4 SiO₂68.1 67.95 66.5 65.1 65.5 65.2 P₂O₅ 1.35 2.25 1.65 1.6 3.05 2.5 TiO₂2.05 2.0 2.0 1.95 2.1 2.05 ZRO₂ 0.95 0.95 0.95 0.95 1.05 1.0 As₂O₃ 0.250.25 0.25 0.25 0.2 0.25 Sum 100.0 100.0 100.0 100.0 100.0 100.0 SiO₂ +(5xLi₂O) 110.60 110.95 109.75 108.85 110.50 108.70 MgO + ZnO ΣR₂O (R =Na, K, Cs, Rb) 2.25 2.1 2.15 1.85 0.75 0.8 ΣRO (R = Ca, Ba, Sr) 0.45 0.71.2 2.0 2.5 3.10 Va [° C.] 1312 1318 1292 1271 1275 Ceram. temperature[° C.] 760 780 780 760 780 770 Ceram. time [days] 2.5 2.5 2.5 2.5 2.52.5 Cryst. phase [% by vol.] 53 54 53 49 64 57 Cryst. size [nm] 39 40 4542 40 40 Av. CTE(0; +50° C.) [ppm/K] 0.05 0.07 0.10 0.10 −0.03 0.01 TCL(0; +50° C.) 2.47 3.41 5.22 5.1 1.64 0.57 |Expansion at 50° C.| 2.473.41 5.22 5.1 1.64 0.57 Index F 1.00 1.00 1.00 1.00 1.00 1.00 Hyst @ 45°C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 35° C. [ppm] <0.1 <0.1<0.1 <0.1 <0.1 <0.1 Hyst @ 30° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 <0.1Hyst @ 22° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 10° C. [ppm]<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ +5° C. [ppm] <0.1 <0.1 <0.1 <0.1<0.1 <0.1 Hyst @ 0° C. [ppm] 0.1 Hyst @ −5° C. [ppm] 0.16 Ceram.temperature [° C.] 760 780 780 760 800 780 Ceram. time [days] 2.5 2.52.5 2.5 2.5 2.5 Av. CTE (−30; +70° C.)[ppm/K] 0.03 0.06 0.09 0.08 0.020.01 Av. CTE (−40; +80° C.)[ppm/K] 0.02 0.05 0.08 0.08 0.004 0.006Example No. (Ex.) 7 8 9 10 11 12 Li₂O 9.15 9.0 8.9 9.25 8.35 9.3 Na₂O0.6 0.45 0.1 1.1 0.8 K₂O 0.9 0.5 0.65 0.2 MgO ZnO CaO 0.95 2.5 2.5 1.81.1 BaO 0.55 0.6 0.85 1.4 SrO 0.6 0.8 Al₂O₃ 17.95 17.3 17.2 18.35 17.417.9 SiO₂ 64.0 63.05 64.55 62.55 66.35 64.1 P₂O₅ 2.6 3.85 2.9 3.35 0.82.85 TiO₂ 2.05 2.05 2.1 2.05 2.0 2.15 ZRO₂ 1.0 1.05 1.05 1.05 1.0 1.05As₂O₃ 0.25 0.25 0.25 0.25 0.25 0.25 Sum 100.0 100.0 100.0 100.0 100.0100.0 SiO₂ + (5xLi₂O) 109.75 108.05 109.05 108.80 108.10 110.60 MgO +ZnO ΣR₂O (R = Na, K, Cs, Rb) 1.50 0.95 0.75 1.1 1.0 ΣRO (R = Ca, Ba, Sr)1.5 2.5 3.1 2.4 2.75 1.4 Va [° C.] 1267 1256 1258 1248 Ceram.temperature [° C.] 810 800 800 810 780 820 Ceram. time [days] 2.5 2.52.5 2.5 2.5 2.5 Cryst. phase [% by vol.] 58 62 64 64 52 60 Cryst. size[nm] 48 47 45 46 47 47 Av. CTE(0; +50° C.) [ppm/K] 0.007 0.06 −0.08−0.08 −0.03 −0.08 TCL (0; +50° C.) 0.37 3 3.88 3.89 1.34 3.96 |Expansionat 50° C.| 0.37 2.88 3.78 3.89 1.34 3.96 Index F 1.00 1.04 1.03 1.001.00 1.00 Hyst @ 45° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 35°C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 30° C. [ppm] <0.1 <0.1<0.1 <0.1 <0.1 <0.1 Hyst @ 22° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 <0.1Hyst @ 10° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ +5° C. [ppm]<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 0° C. [ppm] <0.1 <0.1 <0.1 Hyst @−5° C. [ppm] <0.1 0.15 <0.1 Ceram. temperature [° C.] 820 780 800 810780 820 Ceram. time [days] 2.5 2.5 2.5 2.5 2.5 2.5 Av. CTE (−30; +70°C.)[ppm/K] 0.03 0.006 −0.08 −0.07 −0.05 −0.10 Av. CTE (−40; +80°C.)[ppm/K] 0.02 −0.01 −0.10 −0.08 −0.05 −0.1 Example No. (Ex.) 13 14 1516 17 18 Li₂O 9.1 9.35 8.9 8.6 9.05 8.7 Na₂O 0.1 0.45 0.45 0.65 0.6 0.9K₂O 0.6 1.1 0.95 1.65 0.85 0.3 MgO 0.25 ZnO 0.15 0.45 CaO 1.3 1.1 1.250.85 0.65 BaO 1.1 0.4 1.05 0.45 1.15 SrO Al₂O₃ 17.9 18.85 16.95 16.3518.0 18.1 SiO₂ 62.0 61.6 67.15 67.9 63.75 64.0 P₂O₅ 4.6 3.95 1.6 2.752.45 TiO₂ 2.1 2.0 2.05 2.05 2.05 2.1 ZRO₂ 1.05 1.0 1.05 1.0 1.05 1.0As₂O₃ 0.15 0.2 0.2 0.2 0.2 0.2 Sum 100.0 100.0 100.0 100.0 100.0 100.0SiO₂ + (5xLi₂O) 107.50 108.35 111.65 110.90 109.00 107.50 MgO + ZnO 0.400.45 ΣR₂O (R = Na, K, Cs, Rb) 0.70 1.55 1.4 2.3 1.45 1.2 ΣRO (R = Ca,Ba, Sr) 2.40 1.50 2.3 1.3 1.8 Va [° C.] Ceram. temperature [° C.] 790815 815 770 830 815 Ceram. time [days] 2.5 2.5 2.5 2.5 2.5 2.5 Cryst.phase [% by vol.] 62 61 53 52 59 59 Cryst. size [nm] 46 50 46 39 48 48Av. CTE(0; +50° C.) [ppm/K] 0.08 −0.01 0.08 0.04 0.01 −0.015 TCL (0;+50° C.) 4.00 0.58 4.14 2.07 0.61 0.74 |Expansion at 50° C.| 4.00 0.544.14 2.07 0.61 0.74 Index F 1.00 1.07 1.00 1.00 1.00 1.00 Hyst @ 45° C.[ppm] <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 35° C. [ppm] <0.1 <0.1 <0.1 <0.1<0.1 Hyst @ 30° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 22° C. [ppm]<0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 10° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1Hyst @ +5° C. [ppm] 0.11 <0.1 <0.1 <0.1 <0.1 Hyst @ 0° C. [ppm] 0.19<0.1 <0.1 <0.1 0.11 Hyst @ −5° C. [ppm] 0.22 <0.1 <0.1 0.13 0.18 Ceram.temperature [° C.] 790 815 770 820 815 Ceram. time [days] 2.5 2.5 2.52.5 2.5 Av. CTE (−30; +70° C.)[ppm/K] 0.12 −0.02 0.02 −0.06 −0.03 Av.CTE (−40; +80° C.)[ppm/K] 0.11 −0.04 0.01 −0.07 −0.04 Example No. (Ex.)19 20 21 22 23 Li₂O 9.15 8.1 9.35 9.15 8.85 Na₂O 0.55 0.4 0.7 0.45 0.55K₂O 0.85 1.0 0.25 0.6 0.85 MgO 0.30 ZnO 0.20 CaO 0.8 2.25 1.25 0.8 1.0BaO 0.45 1.1 0.8 0.70 SrO Al₂O₃ 17.75 15.45 16.85 16.85 14.45 SiO₂ 64.068.05 64.45 67.35 67.95 P₂O₅ 2.75 1.55 3.35 2.50 TiO₂ 2.0 1.95 3.80 1.95ZRO₂ 1.0 1.0 2.5 1.0 As₂O₃ 0.2 0.25 0.2 0.2 0.2 Sum 100.0 100.0 100.0100.0 100.0 SiO₂ + (5xLi₂O) 109.75 108.55 111.20 113.10 112.20 MgO + ZnO0.5 ΣR₂O (R = Na, K, Cs, Rb) 1.4 1.4 0.95 1.4 ΣRO (R = Ca, Ba, Sr) 1.252.25 2.35 1.7 Va [° C.] Ceram. temperature [° C.] 815 770 810 825 800Ceram. time [days] 2.5 2.5 2.5 2.5 2.5 Cryst. phase [% by vol.] 61 51 6263 59 Cryst. size [nm] 50 33 76 33 42 Av. CTE(0; +50° C.) [ppm/K] −0.0750.07 −0.075 −0.03 0.035 TCL (0; +50° C.) 3.73 3.38 3.75 1.7 1.77|Expansion at 50° C.| 3.73 3.38 3.75 1.7 1.77 Index F 1.00 1.00 1.001.00 1.00 Hyst @ 45° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 35° C.[ppm] <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 30° C. [ppm] <0.1 <0.1 <0.1 <0.1<0.1 Hyst @ 22° C. [ppm] <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 10° C. [ppm]<0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ +5° C. [ppm] <0.1 <0.1 0.12 <0.1 <0.1Hyst @ 0° C. [ppm] 0.14 0.1 0.17 <0.1 <0.1 Hyst @ −5° C. [ppm] 0.21 0.170.21 <0.1 0.11 Ceram. temperature [° C.] 815 770 810 825 Ceram. time[days] 2.5 2.5 2.5 2.5 Av. CTE (−30; +70° C.)[ppm/K] −0.09 0.05 −0.09−0.05 Av. CTE (−40; +80° C.)[ppm/K] −0.10 0.04 −0.10 −0.06

TABLE 2 Compositions, ceramization and properties (mol %) ComparativeExample No. (Comp. Ex.) 1 2 5 6 Li₂O 8.1 9.15 9.45 9.5 Na₂O 0.4 0.4 0.20.1 K₂O 0.15 0.2 0.7 0.55 MgO ZnO CaO 4.15 2.2 0.4 BaO 0.6 1.75 SrOAl₂O₃ 12.45 14.2 16.75 16.6 SiO₂ 72.3 71.7 64.15 65.55 P₂O₅ 0.62 3.3 2.2TiO₂ 1.3 1.75 2.05 2.1 ZRO₂ 1.0 1.2 1.0 1.05 As₂O₃ 0.15 0.15 0.2 0.2 Sum100.0 100.0 100.0 100.0 SiO₂ + (5xLi₂O) MgO + ZnO ΣR₂O (R = Na, K, Cs,Rb) 0.55 0.6 0.9 0.65 ΣRO (R = Ca, Ba, Sr) 4.15 0.6 2.2 2.15 Va [° C.]1345 1340 Ceram. temperature [° C.] 760 800 800 Ceram. time [days] 102.5 2.5 Cryst. phase [% by vol.] 60 66 58 Cryst. size [nm] 63 45 47 Av.CTE(0; +50° C.) [ppm/K] −0.25 −0.27 −0.46 TCL (0; +50° C.) |Expansion at50° C.| Index F Hyst @ 45° C. [ppm] Hyst @ 35° C. [ppm] Hyst @ 30° C.[ppm] Hyst @ 22° C. [ppm] <0.1 Hyst @ 10° C. [ppm] <0.1 Hyst @ +5° C.[ppm] <0.1 Hyst @ 0° C. [ppm] 0.13 Hyst @ −5° C. [ppm] 0.24 Ceram.temperature [° C.] Ceram. time [days] Av. CTE (−30; +70° C.)[ppm/K] Av.CTE (−40; +80° C.)[ppm/K] Comparative Example No. (Comp. Ex.) 7 8 9 1011 12 Li₂O 8.5 7.78 9.32 9.2 9.4 9.0 Na₂O 0.1 0.8 0.1 0.2 0.1 K₂O 0.5MgO 1.8 1.2 1.6 1.2 1.6 ZnO 1.3 1.8 0.4 0.6 0.6 0.4 CaO 2.42 1.0 1.2 1.01.3 BaO 1.07 0.36 0.4 0.3 0.5 SrO Al₂O₃ 16.9 15.39 19.11 16.2 19.0 16.4SiO₂ 64.3 65.42 61.4 63.3 61.4 63.9 P₂O₅ 3.4 2.47 3.97 3.8 3.9 3.5 TiO₂1.9 1.67 1.92 2.2 1.9 2.1 ZRO₂ 1.1 0.92 1.07 1.1 1.1 1.2 As₂O₃ 0.2 0.260.25 0.2 0.2 0.1 Sum 100.0 100.0 100.0 100.0 100.0 100.1 SiO₂ + (5xLi₂O)MgO + ZnO 3.1 1.8 1.6 2.2 1.8 2.0 ΣR₂O (R = Na, K, Cs, Rb) 0.6 0.8 0.10.2 0.1 ΣRO (R = Ca, Ba, Sr) 3.49 1.36 1.6 1.3 1.8 Va [° C.] Ceram.temperature [° C.] 810 760 810 760 Ceram. time [days] 10 10 5 10 Cryst.phase [% by vol.] 76 Cryst. size [nm] 72 Av. CTE(0; +50° C.) [ppm/K]0.03 0.02 0.002 −0.15 0.03 −0.05 TCL (0; +50° C.) 1.19 3.68 1.32 0.35|Expansion at 50° C.| 0.11 3.68 1.28 0.35 Index F 10.82 1.00 1.03 1.00Hyst @ 45° C. [ppm] 0.11 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 35° C. [ppm]0.14 <0.1 0.12 <0.1 <0.1 <0.1 Hyst @ 30° C. [ppm] 0.18 <0.1 0.16 <0.10.1 0.11 Hyst @ 22° C. [ppm] 0.27 0.14 0.24 0.14 0.16 0.17 Hyst @ 10° C.[ppm] 0.61 0.42 0.54 0.38 0.85 0.43 Hyst @ +5° C. [ppm] 0.85 0.61 0.740.56 0.61 0.61 Hyst @ 0° C. [ppm] 1.1 0.81 0.92 0.76 0.85 0.82 Hyst @−5° C. [ppm] 1.2 0.96 1.16 0.93 1.04 0.97 Ceram. temperature [° C.]Ceram. time [days] Av. CTE (−30; +70° C.)[ppm/K] Av. CTE (−40; +80°C.)[ppm/K] Comparative Example No. (Comp. Ex.) 13 14 15 16 Li₂O 8.4 8.29.4 9.3 Na₂O 0.05 0.35 0.1 0.25 K₂O 0.6 0.25 MgO 1.8 ZnO 0.95 1.2 0.60CaO 2.3 2.35 1.0 BaO 0.85 SrO Al₂O₃ 16.55 16.5 17 18.95 SiO₂ 65.15 64.864.4 61.5 P₂O₅ 3.4 3.3 3.5 4.05 TiO₂ 2.0 2.0 1.95 2.05 ZRO₂ 1.1 1.1 1.051.05 As₂O₃ 0.15 0.2 0.2 0.15 Sum 100.0 100.0 100.0 100.0 SiO₂ + (5xLi₂O)MgO + ZnO 0.95 1.2 1.8 0.60 ΣR₂O (R = Na, K, Cs, Rb) 0.05 0.35 0.7 0.50ΣRO (R = Ca, Ba, Sr) 2.25 2.35 1.85 Va [° C.] Ceram. temperature [° C.]770 810 790 830 Ceram. time [days] 5 1 5 2.5 Cryst. phase [% by vol.] 7369 74 66 Cryst. size [nm] 43 47 56 41 Av. CTE(0; +50° C.) [ppm/K] −0.03−0.08 −0.06 0.07 TCL (0; +50° C.) 4.29 |Expansion at 50° C.| 3.55 IndexF 1.21 Hyst @ 45° C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 35° C. [ppm] <0.1<0.1 <0.1 <0.1 Hyst @ 30° C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 22° C.[ppm] 0.13 <0.1 0.16 <0.1 Hyst @ 10° C. [ppm] 0.44 0.3 0.44 0.15 Hyst @+5° C. [ppm] 0.67 0.55 0.63 0.23 Hyst @ 0° C. [ppm] 0.97 0.84 0.85 0.35Hyst @ −5° C. [ppm] 1.3 1.13 1.0 0.5 Ceram. temperature [° C.] Ceram.time [days] Av. CTE (−30; +70° C.)[ppm/K] Av. CTE (−40; +80° C.)[ppm/K]

TABLE 3 Alternative index f_(T.i.) for selected examples and onecomparative example f_(T.i.) Ti-dop. [ppm/K] SiO₂ Ex. 6 Ex. 7 Ex. 12 Ex.14 Ex. 17 Ex. 18 20-40° C. 0.024 0.010 0.009 0.014 0.012 0.016 20-70° C.0.039 0.011 0.010 0.023 0.038 0.014 0.022 −10-30° C.  0.015 0.004 0.0110.006

1. LAS glass ceramic having an average coefficient of thermal expansionCTE in the range from 0 to 50° C. of not more than 0±0.1×10⁻⁶/K andthermal hysteresis at least within the temperature range from 10° C. to35° C. of <0.1 ppm, and comprising the following components (in mol %based on oxide): SiO₂ 60-71  Li₂O 7-9.4 MgO + ZnO  0-<0.6

at least one component selected from the group consisting of P₂O₅, R₂O,where R₂O may be Na₂O and/or K₂O and/or Cs₂O and/or Rb₂O, and RO, whereRO may be CaO and/or BaO and/or SrO, and nucleating agent in a contentof 1.5 to 6 mol %, where nucleating agent is at least one componentselected from the group consisting of TiO₂, ZrO₂, Ta₂O₅, Nb₂O₅, SnO₂,MoO₃, WO₃.
 2. LAS glass ceramic according to claim 1, further containingAl₂O₃ in a content of 10 to 22 mol % and/or P₂O₅ in a content of 0.1 to6 mol %.
 3. LAS glass ceramic according to claim 1, wherein the contentof the sum of ZnO+MgO is ≤0.55 mol % and/or the content of MgO is ≤0.35mol % and/or the content of ZnO is <0.5 mol %.
 4. LAS glass ceramicaccording to claim 1, wherein the content of the sum of ZnO+MgO is ≤0.5mol %.
 5. LAS glass ceramic according to claim 1, wherein the content ofSiO₂ is 60 to ≤70 mol %.
 6. LAS glass ceramic according to claim 1,wherein the content of the sum of RO (CaO+BaO+SrO) is ≥0.1 mol % and/or≤6 mol %.
 7. LAS glass ceramic according to claim 1, wherein the contentof the sum of R₂O (Na₂O+K₂O+Cs₂O+Rb₂O) is ≥0.1 mol % and/or ≤6 mol %. 8.LAS glass ceramic according to claim 1, wherein the content of the sumof nucleating agent is ≥2 mol % and/or ≤5 mol %.
 9. LAS glass ceramicaccording to claim 1, wherein the following condition is applicable:molar content of SiO₂+(5×molar content of Li₂O)≥106 and/or wherein thefollowing condition is applicable: molar content of SiO₂+(5×molarcontent of Li₂O)≤115.5.
 10. LAS glass ceramic according to claim 1,wherein a processing temperature Va is not more than 1330° C.
 11. LASglass ceramic according to claim 1, wherein a main crystal phase is highquartz solid solution, and/or the average crystallite size of the highquartz solid solution is <100 nm and/or a crystal phase content is lessthan 70% by volume.
 12. LAS glass ceramic according to claim 1, whereinan index F is <1.2, where F=TCL (0; 50° C.)/|expansion (0; 50° C.)|. 13.LAS glass ceramic according to claim 1, wherein an alternative indexf_((20;40)) is <0.024 ppm/K and/or an alternative index f_((20;70)) is<0.039 ppm/K and/or an alternative index f_((−10;30)) is <0.015 ppm/K.14. LAS glass ceramic according to claim 1, which has a relative changein length (dl/l₀) of ≤|0.10| ppm within the temperature range from 20°C. to 30° C. and/or a relative change in length (dl/l₀) of ≤|0.17| ppmwithin the temperature range from 20° C. to 35° C.
 15. LAS glass ceramicaccording to claim 1, which has a relative change in length (dl/l₀) of≤10.301 ppm within the temperature range from 20° C. to 40° C.
 16. LASglass ceramic according to claim 1, wherein a CTE-T curve within atemperature interval having a width of at least 30 K has a slope of≤0±2.5 ppb/K².
 17. LAS glass ceramic according to claim 1, havingthermal hysteresis of <0.1 ppm at least within the temperature rangefrom 5° C. to 45° C.
 18. A precision component, especially for use inmetrology, spectroscopy, measurement technology, lithography, astronomyor observation of the Earth from space comprising the LAS glass ceramicaccording to claim 1.